Field of the Invention
The disclosed and claimed concept relates to a can bodymaker and, more specifically, to a can bodymaker wherein the ram assembly includes outboard bearings and a ram body having a reduced length.
Background Information
Generally, an aluminum can begins as a disk of aluminum, also known as a “blank,” that is punched from a sheet or coil of aluminum. That is, the sheet is fed into a dual action press where a “blank” disc is cut from the sheet by an outer slide/ram motion. An inner slide/ram then pushes the “blank” through a draw process to create a cup. The cup has a bottom and a depending sidewall. The cup is fed into one of several bodymakers, which perform a redraw and ironing operation. More specifically, the cup is disposed in a can forming machine at the mouth of a die pack having substantially circular openings therein. The cup is held in place by a redraw sleeve, which is part of the redraw assembly. The redraw sleeve is a hollow tubular construct that is disposed inside the cup and biases the cup against the die pack. More specifically, the first die in the die pack is the redraw die, which is not a part of the redraw assembly. The cup is biased against the redraw die by the redraw sleeve. Other dies, the ironing dies, are disposed behind, and axially aligned with, the redraw die. The ironing dies and redraw die are not part of the redraw assembly. An elongated, cylindrical ram assembly 1, shown in FIGS. 1 and 1A, includes a carriage 2PA that supports a ram body 3PA with a punch 4PA at the forward, distal end. The ram and punch are aligned with, and structured to travel through, the openings in the redraw die and the ironing dies. At the end of the die pack opposite the ram is a domer. The domer is a die structured to form a concave dome in the bottom of the cup/can.
Thus, in operation, a cup is disposed at one end of the die pack. The cup, typically, has a greater diameter than a finished can as well as a greater wall thickness. The redraw sleeve is disposed inside of the cup and biases the cup bottom against the redraw die. The opening in the redraw die has a diameter that is smaller than the cup. The elongated ram body, and more specifically the punch, passes through the hollow redraw sleeve and contacts the bottom of the cup. As the ram body continues to move forward, the cup is moved through the redraw die. As the opening in the redraw die is smaller than the original diameter of the cup, the cup is deformed and becomes elongated with a smaller diameter. The wall thickness of the cup typically remains the same as the cup passes through the redraw die. As the ram continues to move forward, the elongated cup passes through a number of ironing dies. The ironing dies each thin the wall thickness of the cup causing the cup to elongate. The final forming of the can body occurs when the bottom of the elongated cup engages the domer, creating a concave dome in the cup bottom. At this point, and compared to the original shape of the cup, the can body is elongated, has a thinner wall, and a domed bottom.
During this operation, heat is created by friction in both the ram assembly and the die pack. This heat is dissipated by a cooling fluid that passes through and over the surface of the components. The cooling fluid disposed on the surface of the ram body is substantially collected by a seal assembly disposed between a hydrostatic/hydrodynamic bearing assembly and the redraw (or hold down) assembly. The seal assembly includes a number of seals that conform to the cross-sectional shape of the ram body. As the ram body passes through the seal assembly, the cooling fluid is collected and recycled.
After the forming operations on the can body are complete, the can body is ejected from the ram, and more specifically the punch, for further processing, such as, but not limited to trimming, washing, printing, flanging, inspecting and placed on pallets, which are shipped to the filler. At the filler, the cans are taken off of the pallets, filled, ends placed on them and then the filled cans are repackaged in six packs and/or twelve pack cases, etc.
The ram body moves in a cycle many times each minute. To accomplish this motion, the bodymaker also includes a crank assembly having a crank arm. The crank arm is coupled to the ram assembly and causes the ram assembly to reciprocate. The ram body is substantially, axially aligned with the hollow redraw sleeve and the die pack. The alignment is important because a mis-alignment causes the ram to wear on the dies and vice-versa. As shown in FIG. 1A, alignment of the ram body is improved by a hydrostatic/hydrodynamic ram guide assembly 5PA that guides the ram body through the tooling, hereinafter a “ram guide.” There are additional hydrostatic/hydrodynamic fluid bearing assemblies 6PA on the sides of the ram assembly carriage, but these bearings do not “guide” the ram. These hydrostatic/hydrodynamic fluid bearing assemblies 6PA are disposed in channels and have ports 7PA, disposed on the top, side, and lower surfaces, that produce a lubricating fluid. Various factors, such as, but not limited to, the relatively short length of the carriage, wherein the hydrostatic/hydrodynamic fluid bearing assemblies 6PA are immediately adjacent each other, prevent these additional hydrostatic/hydrodynamic fluid bearing assemblies 6PA from controlling the orientation and alignment of the ram body. That is, the small amount of “wobble” of the carriage in the channels prevents the carriage and the hydrostatic/hydrodynamic fluid bearing assemblies 6PA from guiding the ram body.
Thus, as used herein, a “guide,” when used in reference to a ram body bearing, means to control the orientation and alignment of the ram body. Thus, a “guide bearing” or “guide bearing assembly,” as used herein, is structured to, and does, control the orientation and alignment of the ram body. A bearing, such as the prior art hydrostatic/hydrodynamic fluid bearing assemblies 6PA on the sides of the ram assembly carriage, that have a minimal influence or are merely capable of affecting the orientation and alignment of the ram body are not “guide” bearing assemblies, as used herein. Stated alternately, and noting that a ram body must be guided, if the ram body has no guide, then the bearing assemblies on the sides of the ram carriage are the “guide bearing assemblies.” If, however, the ram body has a guide, then the bearing assemblies on the sides of the ram carriage are not “guide bearing assemblies.”
The guide bearing assembly is, typically, disposed immediately upstream (closer to the crank arm) of the redraw assembly. The fluid bearing assembly includes a body defining a passage. The ram body extends through the fluid bearing assembly passage. Moreover, the fluid bearing assembly introduces a fluid, such as, but not limited to oil, between the fluid bearing assembly body and the ram body. Controlling the amount and pressure of the fluid allows for precise control over the alignment of the ram body with the hollow redraw sleeve and the die pack. The fluid bearing assembly fluid is collected by the seal assembly and recycled.
The disadvantage to this configuration is that the fluid bearing assembly fluid is not completely removed by the seal assembly. Thus, a portion of the fluid bearing assembly fluid remains on the ram body when the cooling fluid is applied. Further, the fluids mix and the collected cooling fluid becomes contaminated. This also means that the fluid bearing assembly fluid, which may be an expensive oil, is slowly lost.
Another disadvantage is that the ram body must have a sufficient length not only to extend through the die pack, but the seal assembly and fluid bearing assembly; for a can body of a typical 12 fluid ounce can, the ram body has a length of between about 50 inches to 52 inches when using a 24 inch stroke for a can body of a typical 12 fluid ounce can. Ram lengths differ for different stroke lengths to support different size can bodies. For example, the following is a table of common ram lengths and the associated stroke.
ExemplaryRam Length RangeA Specific EmbodimentStroke Length45.0 to 46.0 Inches45.387 Inches 18 Inches49.0 to 51.813 Inches 50.0 Inches22 Inches50.0 to 52.0 Inches51.0 Inches24 Inches56.0 to 58.0 Inches57.0 Inches30 InchesA ram body of any of these lengths is prone to damage from normal wear and tear.
As noted above, the ram body passes through a die pack in a first direction when forming a can body, and then travels back through the die pack after the can body is formed. The die pack in the bodymaker has multiple, spaced dies, each die having an opening. Each die opening is slightly smaller than the next adjacent upstream die.
Because the openings in the subsequent dies in the die pack have a smaller inner diameter, i.e. a smaller opening, the aluminum cup is thinned as the ram moves the aluminum through the rest of the die pack. The space between the punch and the redraw die is typically a small clearance (0.001-2 inch per side) over metal thickness and is less than 0.004 inch in the last ironing die. Typical aluminum gauge used to create a typical 12 fluid ounce can is 0.0108 inch in practice today. This narrow spacing, however, is a disadvantage, especially during the return stroke.
Ram droop or deflection is inherent to this long slender horizontal ram and punch with stroke lengths varying from 22-30 inches and throughput frequencies ranging from 210 to 450 strokes/minute (SPM) depending on can diameter, can height and machine model. In its simplest form, this ram can be visualized as a cantilever beam fixed at one end and free on the other end. The upper theorized beam type shows the deflection of the ram due to the tungsten carbide punch weight and the lower theorized beam type shows the deflection of the long steel ram due to its own weight. The total deflection of the horizontal ram in a known body maker is a combination of these two effects. The typical weight of the ram and punch assembly is approximately 50 lbf total. The maximum deflection (δ) or ram droop is linearly proportional to the weight (point load P or distributed load ω) of the long slender light weight steel ram (ρsteel=0.284 lb/in3) and heavy tungsten carbide (or WC−ρwc=0.567 lb/in3) punch at the end of the ram. However, the maximum deflection or ram droop (conceptualized as a cantilever beam) is governed by its length (l) to the fourth power for the long slender steel ram and to the third power for the heavy carbide punch at the end of the ram. I is the area moment of inertia, as is known. Therefore, significant reduction in deflection or ram droop can be realized if the ram could be shortened. The concept to outboard the hydrostatic/hydrodynamic ram bearings from the main ram itself is essential to shortening the length of the ram because the ram no longer requires additional length to be supported by the bearing through the can body making process. Ram droop is a problem on the return stroke where a can is not being formed. In the return stroke, the punch and ram have more of a tendency to contact the tooling causing wear and damage. A significant contributor to this is contact between the punch and the ironing dies (primarily third iron or end iron) on the return stroke of the machine.
Further, as noted above, a ram body passes through a hydrostatic/hydrodynamic fluid bearing assembly. The hydrostatic/hydrodynamic fluid bearing assembly is fixed to a bulkhead in the can bodymaker housing assembly. This means that the length of the cantilevered portion of the ram body changes during the body making cycle. That is, when the ram body is in a retracted, first position, the length of the cantilevered portion of the ram body is relatively short. Conversely, when the ram body is in an extended, second position, the length of the cantilevered portion of the ram body is relatively long. The dynamic nature of the length of the cantilevered portion of the ram body means that the amount of droop changes dynamically as well. This means that a system to compensate for the ram droop would have to be a dynamic system as well.
Further, ram droop, as well as any other contact between the ram body and the die pack cause the ram body to become misaligned with the die pack. Stated alternately, contact between the ram body and the die pack creates an offsetting force acting in various directions about the ram assembly center of gravity. These offsetting forces create a torque about the ram assembly center of gravity resulting in the “wobble” discussed above. This is a disadvantage.
There is, therefore, a need for a ram assembly including a ram body that is less susceptible to ram droop. There is, more specifically, a need for a ram body having a reduced length. That is, the length of the ram body is a stated problem.